Full dose or half dose? Clearing up confusion over Moderna boosters
It is now official: the first batch of Moderna vaccine will land in Thailand by November 5. However, before rushing out to get a jab, you need to know a few things – including that a Moderna booster shot may contain just half the normal dose.
As of Sunday (October 24), nearly 40 million people in Thailand had received at least one anti-COVID injection, while 28.4 million were double-jabbed. Many of these people opted to get vaccinated while waiting for the Moderna doses to arrive. So, how much Moderna vaccine will they need as a booster?
General advice on booster shots still varies, and many experts caution against getting over-vaccinated. However, some private hospitals are proposing to administer the full 100-microgram (mcg) Moderna shot as a booster for people who received their second shot of another COVID vaccine several months ago.
Meanwhile, Chulabhorn Royal Academy (CRA) has announced that its Moderna booster shots will only carry half the normal dose or 50mcg.
Moderna vaccine for Thailand
Dr. Chalermchai Boonyaleepun, deputy chair of the Senate committee on public health, says people who have paid for their Moderna shot via private hospitals will get the full 100mcg dose. This dosage level is standard for the first and second Moderna shots.
The Government Pharmaceutical Organization (GPO) has procured about 8.7 million Moderna doses in collaboration with the Private Hospital Association and Zuellig Pharma Thailand.
These doses have been sold to private hospitals at Bt1,100 per unit, and the hospitals have sold them on to consumers for between Bt1,500 and Bt2,000 per dose.
CRA, however, is offering the 50mcg Moderna booster for just Bt555.
October 23, 2021 The first 560,000 doses of Moderna vaccine are expected in Thailand by November 5th, according to Zuellig Pharma (ZP) Therapeutics Company, the supplier and distributer of Moderna vaccine in Thailand. In a statement issued today (Saturday), the company said it is ready to take delivery of the first batch of the mRNA vaccine, adding that it will have them distributed immediately.
What is the right dose?
In the United States, a Moderna COVID-19 booster comprises half a dose (50mcg) and is administered at least six months after the first two shots.
However, this half-dose booster is only given to people who have been double-jabbed with Moderna. Also, the US Food and Drug Administration only recommends a Moderna booster for people aged over 65 or those at high risk.
In Thailand, nobody has received two doses of Moderna. To date, the government has offered only Sinovac, AstraZeneca, and Pfizer vaccines, either straight up or as a mix-and-match cocktail. Pfizer, which has only just arrived in Thailand, is being administered mainly to medical workers and children aged 12 to 18. Both Pfizer and Moderna vaccines are made using the new mRNA technology.
Mahidol University’s Faculty of Medicine Siriraj Hospital recommends a half-dose Pfizer booster for those who have received two jabs of either AstraZeneca or Sinovac.
Less is more?
In early trials of Moderna vaccine, participants received one of three dose levels – 25mcg, 100mcg, and 250mcg. The highest dose proved to be too toxic, while the lowest dose elicited the weakest immune response. The 100mcg dose appeared to offer the best balance, triggering strong immunity with acceptable side effects. This 100mcg dose eventually became the one authorized for mass usage across the world.
However, Moderna researchers later found that a 50mcg half-dose could be as effective at stimulating immunity as the full dose. To find out if the low dose offered strong protection, scientists analyzed blood from 35 volunteers who had received two 25mcg shots 28 days apart.
Six months after the second jab, nearly all 35 volunteers had developed “neutralizing” antibodies that block the virus from infecting healthy cells. The volunteers’ blood also contained an armada of different T-cells – “killer” cells that destroy infected cells and a variety of “helper” cells that aid in the development of immunity.
Levels of both antibodies and T-cells were comparable to those with natural immunity after recovering from COVID-19.
By Thai PBS World’s General Desk